The State Administration of Radio Film and Television issued the China mobile multimedia broadcasting (CMMB) industry standard in October, 2006, which adopts the orthogonal frequency division multiplexing (OFDM) technique. The OFDM technique is a known multi-carrier modulation technique, and main principle of the OFDM technique is: dividing a channel into a plurality of orthogonal sub channels, converting the high-speed data into concurrent low-speed sub data streams, and modulating the low-speed sub data streams to each orthogonal sub channel for transmission. In the receiving end, a correlation technique can be adopted to separate orthogonal signals, thereby reducing the interference with each other among the orthogonal sub channels. The bandwidth of each orthogonal sub channel is less than the correlated bandwidth of the channel, and hence, each orthogonal sub channel can be considered as flat fading, thereby the interference among symbols being able to be eliminated. Furthermore, since the bandwidth of each orthogonal sub channel is only a small part of bandwidth of the original channel, so the channel equalization becomes easy relatively. The OFDM has been used in a plurality of wireless system standards at present, such as the Europe digital audio and digital video broadcast systems (DAB, DVB-T, and DVB-H), and 5 GHz high data speed wireless LAN (IEEE802.11a, HiperLan2, MMAC) systems and so on.
The CMMB system proposed a new physical layer frame structure, as shown in FIG. 1, wherein one radio frame includes 40 time slots, and each time slot includes one beacon and a plurality of OFDM symbols. FIG. 2 provides a schematic diagram of a beacon structure in each time slot in a frame structure of the physical layer of the CMMB system, wherein one beacon is composed of one transmitter identification sequence (TxID) and two same synchronization signals (SYNC). The time duration of each synchronization signal is 204.8 microseconds.
The synchronization problem is a practical problem which should be solved by any one communication system at first, and the performance of the synchronization directly affects the performance of the whole communication system. It is unable to have reliable data transmission without a robust and correct synchronization algorithm. The OFDM synchronization process usually includes two processes of a coarse synchronization and a fine synchronization. The coarse synchronization is to use a sliding autocorrelation at first, and then search the peak value of the sliding autocorrelation to obtain a coarse synchronization position; and the fine synchronization is generally obtained by detecting the first effective path of a channel impulse response after obtaining the coarse synchronization position.
In the synchronization algorithm in the related art, it usually adopts the coarse synchronization plus the fine synchronization for each synchronization symbol to obtain the synchronization position, and the calculation complexity of the synchronization algorithm is high. Besides, an abnormal value will appear when the deep fading occurs on the synchronization symbol, and therefore, the existing synchronization method is not stable enough.